1. Field of the Invention
The present invention relates to a data transmission system, a data transmission method, and a media apparatus.
2. Related Art
Audio devices and video devices (to be referred to AV devices hereinafter) are coupled to each other through a network and exchange video data or audio data with each other. In order to couple the AV devices to perform data transfer between the AV devices, some protocol is necessary. For example, a protocol such as IEEE (The Institute of Electrical and Electronics Engineers) 1394 scheme using a serial bus, HTTP (Hyper Text Transport Protocol), or RTSP (Realtime Streaming Protocol) is known. HTTP and RTSP are defined on TCP/IP protocol on an IEEE802 network.
Protocols used in the AV devices are various. Therefore, devices using various protocols can be arranged on the same network. Therefore, a procedure that controls transmission of data between the AV devices on the network is required to be compatible with the various protocols. One that realizes the procedure is a Universal Plug and Play (UPnP) protocol. In particular, a UPnP AV protocol is developed to associate the AV devices with each other.
In the UPnP AV protocol, AV data transmission between the AV devices is performed by using the concept of a virtual connection. Although the virtual connection is associated with actual transmission path or input/output plugs of the devices, the virtual connection is treated in the UPnP AV protocol in a way that the virtual connection does not depend on actual transmission path or transmission protocols. AV data transmission and control performed by the UPnP AV are managed by using the virtual connection.
However, a conventional virtual connection used in the UPnP AV is not always related to actual AV data transmission. For this reason, it is frequent that the management and the control of the AV data transmission cannot be effectively performed.
For example, in an IEEE1394 protocol, communication is performed by establishing a continuous connection between an input plug of an AV device and an output plug of another AV device. In this case, the real connection and a virtual connection can be easily related to each other. This is because a real connection is established in advance, and a virtual connection can be related to the real connection. More specifically, it can be understood that both the ends of the virtual connection are related to the input plug of an actual AV device and the output plug of another actual AV device, and it can be understood that data transmission is performed in a period in which a real connection continues so that the virtual connection also continues.
On the other hand, in an HTTP protocol, when a virtual connection is established, any real connection is not established. When a SetAVTransportURI( ) action of an AV Transport service of UPnP AV is performed after establishment of a virtual connection, a Play action is then performed, and a transmission request is then issued from a reproduction side or a transmission side of AV data transmission, the real connection is established. In establishment of a real connection, the virtual connection and the real connection can be related to each other on the basis of a virtual connection ID and a URI which are arguments of the SetAVTransportURI action in a media renderer or a media server, on the basis of control performed by a control point.
This problem has been pointed out. For example, in Chapters 5.4 to 5.6 of a reference “Designing a UPnP AV Media Renderer v1.0 Intel Corporation, 2003”, it is described that a virtual connection and a real connection must be related to each other. However, any concrete method is not described in the reference. In addition, in section 5.14.1 of a reference “Designing a UPnP AV Media Server v1.0 Intel Corporation, 2003”, it is described that when HTTP_GET is used in delivery of content, a virtual connection and a real connection cannot be related to each other. Japanese Patent Application Laid-open No. 2002-304333 “TRANSMISSION METHOD AND TRANSMISSION APPARATUS” explains procedures of content search, content transmission, and content reproduction which are employed in the UPnP AV. This reference does not refer to any relating between a virtual connection and a real connection.